Johnson wrote on Instagram that he was leaving a workout when he noticed "these kids in the rearview mirror screamin' & runnin' after my truck. Thought to myself, "Should I stop or keep drivin?'" I stopped.

"I hop out of my truck and this kid runs up to me, hugs the hell outta me and says it's been his life's dream to meet me and tell me how much I've inspired him to fight cancer (Hodgkin's lymphoma) and hard core chemo and stem cell transplant treatments."

"He was a little teary eyed and said for months and months all he's wanted to do was find me and say this face to face," Johnson continued. "I told him what it meant to me to hear this story. I thanked him, hugged him (and his friends), got back in my truck and drove away.

"As I'm drivin' I start shaking my head (and tearing up) at how fragile life is and how amazing and cool the universe was to make this meeting happen between myself and this special kid Nick Miller. Let's always take a moment to count our blessings ... cause there's always something to be grateful for."

Dwayne Johnson poses in front of one of the lion statues by Nelson's column on Trafalgar Square in central London, during a photo call for the film Hercules, Wednesday, July 2, 2014. (Photo by Joel Ryan/Invision/AP)